United Kingdom Trial of Radioiodine Intervention for Subclinical Hyperthyroidism

Subclinical hyperthyroidism (SH) is a state of mild thyroid gland overactivity, defined by measurement of thyroid hormones in the blood. It is quite common, affecting about 2% of elderly people. Rather like high blood cholesterol levels, most people have no symptoms of SH, but it is associated with an increased risk of vascular disease. The problem is that we don`t know whether treating SH is worthwhile, in terms of benefit to vascular disease rates and other problems.
We will carry out a trial comparing radioiodine treatment of the thyroid gland overactivity to standard therapy for cardiac risk factors in patients with SH. We will follow people with SH for 5 years after the treatment to find out whether this improves the rate of vascular diseases and other problems. This trial will form the first randomised study of treatment for this condition and will inform healthcare decision making for about 200,000 elderly people each year in the UK.

Overt and subclinical thyroid diseases are emerging as major, but largely unrecognised, cardiovascular risk factors. However, there is little evidence-base to support clinical practice in this increasingly important area (1). Subclinical hyperthyroidism affects about 2% of the elderly population, and is associated with increased morbidity and mortality (2,3). We propose a multi-centre, open, randomised trial of 400MBq of radioactive iodine (131-I) for subjects over 65 years of age with sustained subclinical hyperthyroidism. The primary endpoint is a composite of circulatory mortality, non-fatal MI, non-fatal stroke and revascularisation procedure, and this will be ascertained for 5 years. Secondary endpoints are all-cause mortality, atrial fibrillation, progression to overt hyperthyroidism and fracture. This investigation will provide robust data to support evidence-based, effective and efficient clinical practice for this common condition.